The present invention is concerned with improvements in foundry technology and more specifically relates to the production of foundry molds such as flaskless molds made up of two halves of wet casting foundry sand with tall mold bodies or closely placed mold ribs as for example for an electric motor housing provided with cooling ribs. In the production of such a mold the sand is firstly introduced by vacuum blasting into the mold making cavity, compacted by the pneumatic impact principle and then mechanically pressed while at the same time air is aspirated from the sand.
Such a method of mold production has been previously proposed in the German Pat. No. 2,844,464. Since however the machines proposed in this patent were only designed for producing mold halves with flasks, the rational use of such machines would only be possible with a pair of machines with mold transfer and mold assembly equipment for handling the mold halves produced by them.
The German Pat. No. 3,304,148 has proposed a method making possible the production of upper and lower mold halves in a single flaskless mold making machine having a mold producing device with the two halves of a pattern on its two respective sides. This mold making machine had a pattern plate carrier divided by vertical partitions into two chambers which were able to be separately subjected to vacuum or the action of compressed air. It was not however designed for compaction by pneumatic impact.
In compaction by pneumatic impact a sand-free space comes into existence between the shot blasting grating or the pressing platen (through which the compressed air is admitted) and the back side of the compacted mold.
In such a case the outline of the back of the mold generally matches the side of the mold adjacent to the pattern. For molds with flasks this is unimportant, because for the production of such molds a filling frame is used as a rule and after it has been removed the back side of the mold is strickled until it is at the same level as the edge of the flask.
In the case of flaskless molds the situation is different. A substantial profitability factor here is the possibility of adapting the level of the mold component individually to the respective level of the pattern by programmed level adjustment of the blasting head or heads on a vacuum mold making machine, with the result that there is a substantial saving in sand. However the thin cover of sand on the lowest parts of the pattern possible with such a method makes it necessary to have a highly planar form of the back side of the mold in order to ensure that the flaskless molds resting on pallets are not deformed or broken open. It is more especially in the case of mold parts without a lower opening that it is not always possible to produce such an accurately planar form with blasting and pressing gratings as so far in use.